Reflex camera

ABSTRACT

A reflex camera capable of automatic focus adjustment comprises a motor for driving a lens used for focus adjustment, an electromagnet for lifting-up a mirror to expose a film at the time of shutter release, a battery for operating the motor and the electromagnet, and a controller for controlling power supply such that the power is supplied to the magnet after the lens is moved by the motor to a position such as an in-focus point. Since the power is supplied to the electromagnet after the completion of power supply to the motor, there is no possibility of malfunction of the electromagnet.

This application is a continuation of application Ser. No. 352,548,filed May 12, 1989, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reflex camera having automatic focusadjusting function in which a lens for adjusting focus is driven to anin-focus point corresponding to a result of focus detection. Morespecifically, the present invention relates to a reflex camera in whichmalfunctions are prevented.

2. Description of the Related Art

Basically, a camera having automatic focus adjusting function is adaptedto be operated in a one shot AF mode in which focus adjustment is lockedonce an in-focus condition has attained. When the one shot AF mode isemployed, a focus priority release mode is also used, in which theshutter is not released until the in-focus condition is realized.Therefore, in a conventional camera having automatic focus adjustingfunction, the lens has been driven to and kept at the in-focus pointwhen the shutter is released.

However, in a camera having automatic focus adjusting function in whicha continuous photographing mode for taking photographs continuously anda prediction mode in which the lens is driven while predicting themovement of an object are both used, the driving of the lens should becarried out during a release sequence. In a reflex camera, anelectromagnet is rendered conductive for displacing a mirror from anoptical axis of a photographic lens during the release sequence. If themotor for driving the lens is being driven while the electromagnet isrendered conductive, malfunctions such as failure of mirror lifting-upmay possibly occur, since sufficient current cannot be supplied to theelectromagnet.

SUMMARY OF THE INVENTION

Therefore, one object of the present invention is to prevent the lensdriving for automatic focus adjustment from disturbing mirror lifting-upoperation in a release sequence in a reflex camera.

Another object of the present invention is to prevent operation of onepart from affecting operation of other parts in a reflex camera.

A further object of the present invention is to prevent defocus causedby inertia of a motor for automatic focus adjustment in a reflex camera.

The above described objects of the present invention can be attained bya reflex camera of the present invention, comprising: a first actuator;a second actuator; a battery for supplying electric power to the firstand second actuators; an interrupter for interrupting the power supplyto the first actuator and a controller for controlling the interruptersuch that the power supply to the first actuator is interrupted when thesecond actuator is actuated.

Since the reflex camera comprises the above described components, thefirst and second actuators are not both operated simultaneously.Therefore, parts attached to respective actuators are not simultaneouslyoperated. Consequently, operation of one part does not affect operationof other parts in a reflex camera.

According to another aspect of the present invention, the reflex cameracomprises: a first actuator; a second actuator; a battery for supplyingelectric power to the first and second actuators; an interrupter forinterrupting the power supply to the first actuator; a controller forcontrolling the interrupter such that the power supply to the firstactuator is interrupted when the second actuator is actuated; a drivenmember driven by the first actuator; a monitor apparatus detecting anamount of movement of the driven member to output a detection signalwhen the amount of movement reaches a prescribed value; and a movementstopping apparatus responsive to the detecting signal for stopping themovement of the first actuator.

Since the reflex camera comprises the above described components, evenif the driven member is moved by inertia, the driven member can bestopped since the first actuator is stopped by the movement stoppingapparatus. Consequently, assuming that the first actuator is the motorfor automatic focus adjustment and the driven member is a lens, defocusderived from inertia of the motor for automatic focus adjustment can beprevented in a reflex camera.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

FIG. 1 is a side view of a camera embodying the present invention;

FIG. 2 is a front view of the camera of FIG. 1;

FIG. 3 is a circuit diagram of a control system incorporated into thecamera of FIG. 1;

FIGS. 4 and 5 are time charts explaining the operation of the camera ofFIG. 1;

FIGS. 6A to 13 are flow charts explaining the operation of the camera ofFIG. 1; and

FIG. 14 is a flow chart explaining another embodiment of the operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A camera in a preferred embodiment according to the present inventionwill be described hereinafter with reference to the accompanyingdrawings.

Referring to FIG. 1, a single-lens reflex camera comprises a camera body101 and an interchangeable zoom lens (photographic lens) 102. Containedin the camera body 101 are a main mirror 103, a submirror 104, a focusdetecting module 105, and a mechanism 106 for a series of automaticoperations for lifting up the mirrors 103 and 104, exposure, filmwinding and film rewinding. The mirrors 103 and 104, the focus detectingmodule 105 and the mechanism 106 are not directly related with thepresent invention, and hence the description thereof will be omitted.FIG. 2 is a front view of the camera body 101. The main mirror 103 has areflective portion and a semitransparent portion. Most part of lightpassed through the photographic lens 102 is reflected by the reflectiveportion of the main mirror 103 toward an optical system of the finder,not shown. The rest part of the light passed through the photographiclens 102 passes through the main mirror 103, falls on the submirror 104and is reflected by the submirror 104 toward the focus detecting module105.

FIG. 3 is a circuit diagram of an electronic circuit employed in thecamera of the present invention. Referring to FIG. 3, the controlcircuit comprises a central processing unit 20 (hereinafter abbreviatedto "CPU"), i.e., a microcomputer, for controlling the sequentialoperation of the camera, exposure calculation and automatic focusingoperation, a focus detecting unit 202 for detecting the amount ofdefocus, a display unit 203, such as liquid crystal display LCD or alight emitting diode display LED, a photometric unit 205 for measuringthe brightness Bv of an object, a film sensitivity read unit 206 forautomatically reading the sensitivity of a loaded film, a sequence motorM₁ for winding-up and rewinding the film, an AF motor M₂ for driving thephotographic lens for automatic focusing, and a driver controller 207for energizing magnets for exposure operation and the motors M₁ and M₂.Information provided by a lens data circuit 204 in the interchangeablelens 102 includes lens data such as a full open diaphragm aperturevalue, a maximum diaphragm aperture value, a focal length and aconvergence efficiency (coefficient to exchange defocus amount torevolution of the motor M₂). Information of the display 203, the lensdata circuit 204, the photometric unit 205 and the film sensitivity readunit 206 is applied in serial signals through a serial data bus 201b tothe serial I/O unit 201c of the CPU 201. The lens data is transferred tothe camera body 101 by electric contacts provided near a lens mount whenthe interchangeable lens 102 is mounted on the camera body 101.

The CPU 201 has data buses and input and output terminals P1 to P21. Thefocus detecting unit 202 comprises a linear self-scanning image sensingelement CCD, a CCD driver, an A/D converter and a reference voltagesource for A/D conversion. Image signals obtained by the CCD are giventhrough an automatic focusing data bus (hereinafter referred to as "AFdata bus") 201a to the CPU 201. The display unit 203 displaysinformation provided by the CPU 201 including the results of calculationfor automatic exposure, such as shutter speed Tv and an diaphragmaperture value Av, focusing condition (in-focus/out-of-focus) or aphotographing mode. The photometric unit 205 for measuring thebrightness Bv of an object comprises a photoelectric element forreceiving light, an A/D converter, a reference voltage source for A/Dconversion, and a data I/O circuit connected to the CPU 201. Thephotometric unit 205 measures light transmitted through the photographiclens upon the reception of a light measurement instruction from the CPU201. The film sensitivity read unit 206 reads the film sensitivity ofthe loaded film indicated on the film cartridge through electriccontacts provided in a film chamber (not shown) of the camera body 101.The driver controller 207 is controlled by signals given thereto fromthe CPU 201 through control signal lines CMD0 to CMD8 connected to theoutput terminals P8 to P16 of the CPU 201, respectively. Each of theswitches SW1 to SW3 and SW5 to SW10 has its one end connected to theground. The other end of respective switches is connected to the inputterminals P1 to P7, P20 and P21 of the CPU 201, respectively. The switchSW1 is closed upon the start of a film winding-up operation and isopened upon the completion of the film winding-up operation. The switchSW2 is closed upon the lift-up operation of the mirror 103 and is openedupon the completion of cooking the shutter mechanism. The switch SW3repeats alternate closing and opening operations several times duringthe film winding-up operation by one frame. When a shutter releasebutton, not shown, is pressed to a first position, the switch SW5 isclosed, and then the CPU 201 provides a signal to start a photometricoperation and a focus detecting operation. While the switch SW5 isclosed, the lens 102 is driven for focusing when the lens 102 is at anout-of-focus condition. When the lens 102 is brought into an in-focusposition, the lens driving operation is stopped. If the shutter releasebutton is released to open the switch SW5 before the lens 102 is broughtinto an in-focus position, the focusing operation is interrupted. Theswitch SW6 is a shutter release switch which is closed when the shutterrelease button is pressed further to a second position. When the switchSW6 is closed during the camera being set ready for a photographicoperation, the CPU 201 provides a signal to start a shutter releaseoperation. The switch SW5 is held closed while the shutter releaseswitch SW6 is closed. The switch SW7 is disposed in a film passage todetect a film. The switch SW7 is opened while at least a part of a filmis at a position corresponding to the switch SW7 on the film passage andis closed when no part of the film is at the position corresponding tothe switch SW7. When the film is almost rewound to remain the leadingend of the film slightly from the film cartridge, the switch SW7 changesfrom an OFF state into an ON state. Accordingly, the switch SW7 is afilm cartridge detecting switch disposed near the electric contacts ofthe film sensitivity read unit 206 provided in the film chamber of thecamera body 101. The switch SW8 is closed when a film cartridge isplaced in the film chamber and a back lid of the camera body 101 isclosed. When the film chamber is empty, the switch SW8 is opened. Theswitch SW9 is a back lid detecting switch which is closed when the lidis closed perfectly. The switch SW10 is a multiple exposure modeselector switch which is closed to select a multiple exposure mode.

The reset terminal RESET of the CPU 201 is pulled up to a power supplyvoltage +V_(DD) by a resistor R1. The CPU 201 is reset after the samehas been connected to a power supply thereto in response to a levelchange of a capacitor C₁ from "LOW" to "HIGH" charged through theresistor R1. A quartz oscillator X is connected to the CPU 201 to applyclock signals to the CPU 201.

The driver controller 207 and other controllers will be describedhereinafter. A magnet 1CMg is energized to hold a preceding shuttercurtain when a control signal output line 1CMGO becomes "LOW". A magnet2CMg is energized to hold a trailing shutter curtain when a controlsignal output line 2CMGO becomes "LOW". A time interval between therelease of the preceding shutter curtain and the release of the trailingshutter curtain corresponds to a shutter speed. A magnet FMg holds adiaphragm stopping member for stopping the diagram of the photographiclens 102. When a control signal output line FMGO becomes "LOW", themagnet FMg is energized to hold a diaphragm stopping member (not shown).When released, the diaphragm stopping member stops the diaphragm at adesired opening. A magnet RMg controls a shutter release member. When acontrol signal output line RMGO is maintained "LOW" for a predeterminedtime, shutter release member is released, the opening of the diaphragmis reduced and the mirrors 103 and 104 are lifted up.

Driving transistors Q1 to Q10 are provided in a driving circuit fordriving the sequence motor M₁ and the AF motor M₂. The sequence motor M₁is provided with two coils respectively for a high-torque low-speedoperating mode and a low-torque high-speed operating mode. The operatingmode of the sequence motor M₁ can be changed between the two operatingmodes. The transistors Q1 to Q6 are connected to enable both the normaland reverse rotation of the sequence motor M₁ in both operating modes.The high-speed operation terminal H, the low-speed operation terminal Land the common terminal C of the sequence motor M₁ are connectedrespectively to the junction of the transistors Q1 and Q2, the junctionof the transistors Q3 and Q4, and the junction of the transistors Q5 andQ6. Tabulated in Table 1 is the condition of the transistors Q1 to Q6and the corresponding mode of operation of the sequence motor M₁.

                  TABLE 1                                                         ______________________________________                                        Q1   Q2      Q3     Q4   Q5    Q6   Operating mode of M.sub.1                 ______________________________________                                        OFF  OFF     OFF    ON   ON    OFF  Low-speed, Normal                         OFF  OFF     ON     OFF  OFF   ON   Low-speed, Reverse                        OFF  ON      OFF    OFF  ON    OFF  High-speed, Normal                        ON   OFF     OFF    OFF  OFF   ON   High-speed, Reverse                       OFF  OFF     OFF    OFF  OFF   OFF  Stop                                      OFF  OFF     ON     OFF  ON    OFF  Low-speed brake                           ON   OFF     OFF    OFF  ON    OFF  High-speed brake                          ______________________________________                                    

In this embodiment, a high-speed brake is not used and only thelow-speed brake SBR is used. In the following description, the low-speedbrake is referred to simply as "brake".

Driving transistors Q7 to Q10 are provided in a driving circuit fordriving the AF motor M₂. The driving transistors Q7 to Q10 are connectedto form a bridge circuit for driving the AF motor M₂ for the normalrotation and the reverse rotation. When the AF motor M₂ is driven forthe normal rotation, the photographic lens is moved forward. When the AFmotor M₂ is driven for the reverse rotation, the photographic lens 102is moved rearward. Switching signals are given through the controlsignal output lines OM1 to OM10 to the transistors Q1 to Q10,respectively.

An diaphragm aperture encoder 211 and an AF encoder 212 comprisephotointerrupters, respectively, and are connected to the drivercontroller 207 by input signal lines PT1 and PT2, respectively. Thediaphragm aperture encoder 211 comprises a light emitting diode 211a anda phototransistor 211b. The diaphragm aperture encoder 211 monitors thestroke of an diaphragm aperture preset lever to determine an opening ofthe diaphragm; that is, the diaphragm aperture encoder 211 detects anopening of the diaphragm when the shutter release switch is closed. Whenthe shutter release is actuated, the light emitting diode 211a emitslight, the phototransistor 211b detects the light emitted by the lightemitting diode 211a and interrupted each time the diaphragm aperturepreset lever moves a unit length, and then the phototransistor 211bgives a detection signal through the input signal line PT1 to the drivercontroller 207 each time the diaphragm aperture preset lever moves aunit length. The driver controller 207 generates a pulse signal byshaping the waveform of the input detection signal and applies the pulsesignal through an output signal line FP to the input terminal P18 of theCPU 201.

The AF encoder 212 comprises a light emitting diode 212a and aphototransistor 212b. The AF encoder 212 monitors the number of rotationof the AF motor M₂ and hence the movement of a focusing lens (not shown)for driving the photographic lens for automatic focusing. Upon thedetection of light emitted by the light emitting diode 212a andinterrupted each time the AF motor M₂ rotates a unit angle, thephototransistor 212b gives a detection signal through an input signalline PT2 to the driver controller 207. The driver controller 207generates a pulse signal by shaping the waveform of the detection signalrepresenting the movement of the focusing lens of the photographic lens102 and applies the pulse signal through an output signal line AFP tothe input terminal P19 of the CPU 201. In this specification, an outputsignal and an output signal line for transmitting the output signal aredenoted by the same designation. The output signal line AFP is connectedalso to the internal counter 201d of the CPU 201 to monitor the presentphotographing position of the photographic lens 102. The counter 201d iscleared when the photographic lens 102 is set in an infinitephotographing position, counts up when the photographic lens 102 isdriven toward a closest photographing position, and counts down when thephotographic lens 102 is driven toward the infinite photographingposition. Thus, a position of the photographic lens 102 from theinfinite photographing position is indicated by the number of pulses.The output signal line AFP is connected further to the interruptterminal, not shown, of the CPU 201. The CPU 201 generates an interruptsignal at the trailing edge of a pulse of the AFP signal.

The CPU is provided internally with a timer 201e and counts time bycounting internal clock signals. The CPU 201 is provided internally withan EEPROM 201f capable of electrical writing and reading and capable ofholding stored data even if a power supply is disconnected therefrom.The CPU 201 is provided with an interrupt timer, not shown, whichgenerates a timer interrupt signal after a set time has elapsed.

Tabulated in Tables 2 and 3 are the condition of control signalsprovided by the CPU 201 and the driver controller 207 and thecorresponding operating modes of the sequence motor M₁ and the AF motorM₂, respectively, in which "H" indicates "HIGH" and "L" indicates "LOW".

                                      TABLE 2                                     __________________________________________________________________________    CPU         Driver Controller Operating mode of                               CMD4                                                                              CMD5                                                                              CMD6                                                                              OM1                                                                              OM2                                                                              OM3                                                                              OM4                                                                              OM5                                                                              OM6                                                                              sequence motor M.sub.1                          __________________________________________________________________________    H   L   L   L  H  L  L  H  H  Low-speed, Normal                               L   H   L   L  H  H  H  L  L  Low-speed, Reverse                              H   L   H   L  L  L  H  H  H  High-speed, Normal                              L   H   H   H  H  L  H  L  L  High-speed, Reverse                             H   H   H   L  H  L  H  L  H  Stop                                            L   L   L   L  H  H  H  H  H  Low-speed brake                                 L   L   H   H  H  L  H  H  H  High-speed brake                                __________________________________________________________________________

                  TABLE 3                                                         ______________________________________                                        CPU       Driver controller Operating mode                                    CMD7  CMD8    OM7    OM8   OM9  OM10  of AF motor M.sub.2                     ______________________________________                                        L     H       L      L     H    H     Normal                                  H     L       H      H     L    L     Reverse                                 H     H       L      H     L    H     Stop                                    L     L       H      H     H    H     Brake                                   ______________________________________                                    

The CPU 201 gives control signals CMD0 to CMD8 through the outputterminals P8 to P16 to the driver controller 207 to control the same. Acontrol signal RMG0 for controlling the magnet RMg and a control signalFMG0 for controlling the magnet FMg are controlled by the controlsignals CMD0 and CMD1, respectively. A control signal 1CMg forcontrolling the magnet 1CMg, and a control signal 2CMGO for controllingthe magnet 2CMg are controlled by the control signals CMD2 and CMD3respectively. Control signals OM1 to OM6 for controlling the sequencemotor M₁ are controlled by control signals CMD4 to CMD6. Control signalsOM7 to OM10 for controlling the AF motor M₂ are controlled by controlsignals CMD7 and CMD8.

A magnet AMg for cancelling holding the film stationary by releasing afilm engagement mechanism (not shown) is connected through a transistorQ11 and a resistor R2 to the output terminal P17 of the CPU 201. Thejunction of the transistor Q11 and the resistor R2 is grounded through aresistor R3. Normally, the output terminal P17 of the CPU 201 is at"LOW"level and the transistor Q11 is OFF, and hence the magnet AMg is notenergized and an element to be attracted is held on the magnet AMg. Whenthe output terminal P17 of the CPU 201 goes "HIGH" to disengage awinding stopper and a winding stopper lever, the magnet AMg is energizedto cancel the attraction of the same.

Sequential steps of a shutter release operation of the embodiment willbe described hereinafter with reference to FIG. 4. The shutter releaseoperation comprises four sequential steps, namely, a mirror liftingstep, an exposure step, a shutter mechanism cocking step # and a filmwinding-up step.

In the mirror lifting step, the main mirror 103 and the submirror 104are retracted and the diaphragm aperture of the photographic lens 102 isstopped down. In the exposure step, the preceding and trailing shuttercurtains of a focal-plane shutter are controlled so as to control anexposure period (shutter speed). In the shutter mechanism cocking step,the main mirror 103, the submirror 104, the diaphragm aperture of thephotographic lens 102, and the preceding and trailing shutter curtainsare biased by springs for the next shutter release operation. In thefilm winding-up step, the film is wound-up to bring the next frame tothe exposure position.

The sequential steps of the shutter release operation will be describedin detail with reference to a time chart shown in FIG. 4.

When the shutter release button is pressed to the second position, theswitch SW6 is closed to start the shutter release operation. Then, theoutput control signal RMGO goes "LOW" and consequently, the releasemagnet RMg is energized, so that the main mirror 103 is retractedtogether with the submirror 104 by the spring to a position near thefinder. Then, the output control signal FMGO goes "LOW" to energize themagnet FMg to start a stopping down operation of the diaphragm biased bythe spring. As mentioned in the previous description given withreference to FIG. 3, the monitoring phototransistor 211b gives a signalrepresenting the stopping down condition of the diaphragm to the drivercontroller 207, and then the driver controller 207 gives an FP signalproduced by shaping the waveform of the signal given thereto by thephototransistor 211b to the CPU 201. Upon counting pulses of the FPsignal corresponding to the diaphragm aperture value and, the CPU 201makes the output control signal FMGO "HIGH" to stop the stopping downoperation of the diaphragm, so that the diaphragm of the photographiclens 102 is set at a desired diaphragm aperture value.

Then, the output control signal 1CMGO, which is "LOW" at the start ofthe shutter release operation, goes "HIGH" to start the exposureoperation. Then, the preceding shutter curtain starts traveling. After apredetermined time interval determined by the exposure calculation, fromthe start of the preceding shutter curtain, the output control signal2CMGO, which is "LOW" at the start of the shutter release operation,goes "HIGH" to start the trailing shutter curtain to terminate exposure.

After the completion of the exposure operation, the shutter mechanismcocking step is started. In the shutter mechanism cocking step, firstthe sequence motor M₁ is driven in a low-speed mode F (L), because thesequence motor M₁ is required to generate a comparatively large torqueat the start. The operating mode of the sequence motor M₁ is changedfrom the low-speed mode F(L) to a high-speed mode F(H), i.e., alow-torque high-speed mode, upon the arrival of the operating speed ofthe sequence motor M₁ at a predetermined value. Thus, the sequence motorM₁ is driven efficiently and the shutter mechanism cocking operation andthe film winding-up operation are carried out rapidly.

The main mirror 103 and the submirror 104 are placed at the lowerposition and are biased by the spring when the sequence motor M₁ isoperated. At the same time, the diaphragm aperture of the photographiclens 102 and the preceding and trailing shutter curtains of the focalplane shutter are biased by the spring. As mentioned above, upon thecompletion of the shutter mechanism cocking operation, the switch SW2 isopened to provide a shutter mechanism cocking operation completionsignal. Upon the detection of the opening of the switch SW2, the CPU 201starts a film winding routine. In the routine, the film restrain member(not shown) is released to start the film winding-up operation and theswitch SW1 for monitoring the film winding-up operation is closed tomaintain the operation of the sequence motor M₁. Upon the completion ofwinding-up the film by one frame, the switch SW1 goes OFF to inform theCPU 201 of the completion of the film winding-up operation. When the CPU201 detects switch SW1 being OFF, it applies a brake to stop thesequence motor M₁. Thus, all the steps of the shutter release operationfor one frame of the film are completed.

Sequential steps of a continuous photographing operation, in which theswitch SW6 remains closed, including a focus detecting operation will bedescribed hereinafter with reference to a time chart shown in FIG. 5. InFIG. 5, periods I and II are for the first and second frames of a film,respectively, in a continuous photographing mode. The operation in theperiod I for the first frame is the same as described with reference toFIG. 4. The main mirror 103 and the submirror 104 must be stabilized atthe lower position for focus detection. To satisfy the requirement,charge accumulation is started after the switch SW2 has been opened anda predetermined lapse of time has passed since the shutter mechanismcocking operation is completed. (in this embodiment, 30 msec). In FIG.5, indicated at I₁ is a time interval for charge accumulation, and at D₁is a time interval corresponding to a data dump time for the A/Dconversion of the pixel data of CCD and storing the converted data inthe memory of the CPU 201. Then, the amount of defocus, the direction ofdefocus and the reliability of focus detection are determined by thepredetermined calculation. The focus detecting operation is not directlyrelated with the present invention and hence the description thereofwill be omitted.

Upon the completion of the first film winding-up operation the switchSW1 is opened to apply the low-speed brake SBR to the sequence motor M₁.At this moment the CPU 201 decides whether or not the switch SW6 isclosed. When the switch SW6 is closed and the continuous photographingmode is selected, the second shutter release operation in the secondperiod II for the second frame is started. In the second shutter releaseoperation, the shutter is released immediately after winding-up thefilm. Therefore, CPU waits for a predetermined lapse of time withlow-speed brake SBR applied to the sequence motor M₁ to enable the filmto stop securely, while the release magnet RMg is energized. When theresults of a focus detecting calculation 1 indicate that thephotographic lens 102 is at an in-focus position, an in-focus photographcan be taken even if the second shutter release operation is startedwith the photographic lens 102 stopped. However, the photograph of thesecond frame will be out-of-focus if the second shutter releaseoperation is carried out without readjusting the photographic lens, whenthe photographic lens is at an out-of-focus position. In most cases inthe continuous photographing mode, in particular, the object is movingand the defocus amount differs depending on time. Accordingly, theamount of defocus resulting from the movement of the object is detectedby the calculation 1. The photographic lens 102 is driven during themirror lifting operation to shift the photographic lens 102 by adistance corresponding to the amount of defocus calculated through thecalculation 1, so that an in-focus photograph can be taken by the secondshutter release operation. AF motor M₂ in FIG. 5 represents the drivingcondition of the photographic lens by AF motor M₂. A single linerepresents that the motor M₂ is OFF and a dual time represents that theAF motor M₂ is in operation for focus adjustment to rotate eitherdirection indicated by the calculation 1. The photographic lens isfurther driven during mirrors 103 and 104 being lifted up for the nextperiod II to correct the defocus detected by the calculation 1. When theoutput control signal RMGO is "LOW", namely, when the release magnet RMgis energized, power is not supplied to the AF motor M₂ to avoid thedeterioration of accuracy of driving the AF motor M₂ or to avoid failurein releasing the main mirror 103 for upward movement due to reduction ofthe current supplied to the release magnet RMg, because the currentsupplied to the release magnet RMg is large and hence the current isreduced if the AF motor M₂ is driven while the release magnet RMg isenergized. Thereafter, the shutter release operation is repeatedcontinuously while the switch SW6 is closed.

The operation of the embodiment will be described hereinafter withreference to flow charts shown in FIGS. 6 to 13.

A control program shown in FIG. 6 is executed when the switch SW5 forstarting the photometric operation is closed. When the switch SW5 isopened, the camera is in a low power consumption mode i.e., a so-calledsleep mode. The switch SW5 is closed to actuate the camera and to startthe clock oscillation. Then, in step #101, the CPU 201 executes astarting procedure to give a start signal and clock signals to theperipheral ICs and to initialize the I/O ports. In step #102, flags andconstants used in the control program are initialized. In step #103, theCPU 201 checks the switches provided on the camera body 101, and carriesout serial communication to and from an electronic flash circuit (notshown), the photographic lens 102 and the display 203. In step #104,unnecessary charges in the CCD are discharged for initialization.

Then, the program goes to step #105 to execute a focus detecting routineCDINTA. Prior to charge accumulation in the CCD, the timer 201e writescharge accumulation start time in a memory TM1 of the CPU 201 in step#106. Then, the counter value of the counter 201d indicating the presentphotographing position of the photographic lens 102 described above isread and stored in a memory T1. In step #107, charge is accumulated inthe CCD to a level appropriate for focus detection. Upon the completionof charge accumulation in step #107, a time measured by the timer 201eis stored in a memory TM2 and the counter value of the counter 201d isstored in a memory T2 in step #108. Then, in step #109, the contents ofa memory TM is stored in a memory TML, and (TM2-TM1)/2 is stored in thememory TM. TM1 is charge accumulation start time, TM2 is chargeaccumulation end time and hence (TM2-TM1)/2 is the central time ofcharge accumulation period (hereinafter, referred to as "accumulationcentral time"). That is, the accumulation central time in the precedingcharge accumulation cycle is stored in the memory TML, and the presentaccumulation central time is stored in the memory TM in step #109.Similarly, the count stored in a memory MI is stored in a memory MIL and(T2-T1)/2 is stored in the memory MI. Since the count corresponds to theposition of the photographic lens as mentioned above, T1 indicates theposition of the photographic lens at the start of charge accumulation,T2 indicates the position of the lens at the end of charge accumulation,and (T2-T1)/2 indicates the position of the lens at the accumulationcentral time. That is, in step #110, the position of the photographiclens at the accumulation central time in the preceding chargeaccumulation cycle is stored in the memory MIL, and the position of thephotographic lens at the present accumulation central time is stored inthe memory MI. In step #111, data dump is executed to transfer the pixeldata of the CCD to the CPU 201. Then, in step #112, the contents of amemory DF0 is stored in a memory LDF before the CPU 201 starts the focusdetecting calculation by using the pixel data. Step #107 for focusdetection has not yet been executed by this moment. Accordingly, in step#112, the amount of defocus DF0 determined in the preceding focusdetecting calculation is stored in the memory LFD. In step #113, thefocus detecting calculation is executed on the basis of the pixel dataprovided by the CCD in step #107 to determine the amount of defocus ofthe photographic lens, the direction of defocus and the reliability offocus detection. Subsequently, in step #114, serial communication andexposure calculation are executed to display the result of photometricmeasurement and to check the condition of the switches. For example,when the switch SW5 is opened in steps #107 to #114, the opening of theswitch SW5 is detected in step #114, and then, the display is cancelledand the motors are stopped to set the camera in the sleep mode. Upon thecompletion of the serial communication and the exposure calculation, aflag VLYF is examined in step #115 to see if the camera is in thecontinuous photographing mode. When the continuous photographing mode isselected during the film winding-up operation, the flag VLFY is set to"1". When VLFY=1, the control program branches off to a continuousphotographing AF routine (step #301), which will be described afterwardwith reference to FIG. 9.

When the flag VLFY=0, step #116 is executed to see if the photographiclens 102 is in the in-focus state. It is decided that the photographiclens is in-focus when the reliability of focus detection determined instep #113 is higher than a predetermined value and the amount of defocusDF0 is less than a predetermined limit value of defocus (in thisembodiment, 100 μm), which may be stored beforehand in the EEPROM 201fof the CPU 201. The limit value of defocus may be decided taking intoconsideration the diaphragm aperture value of the photographic lens andthe corresponding depth of focus by using:

    60 μm+8 x (21og.sub.2 F.sub.No +1)

where F_(No) is an diaphragm aperture value expressed by an F number. Acomparatively small limit value of defocus is selected for focusing at ahigh accuracy, and comparatively large limit value of defocus isselected for rapid focusing. Thus, the limit value of defocus may bedetermined according to the needs of the user.

When a decision is made in step #116 that the photographic lens is inin-focus, an in-focus state is indicated in step #117. Subsequently, theexposure calculation is executed again and the serial communication isperformed to reflect the results of focus detection on the exposurecalculation. In step #119, a query is made to see if the switch SW6 isclosed. The serial communication is repeated in step #120 until theresponse in step #119 becomes affirmative.

When the decision in step #116 is negative, the control program jumps tostep #121 to execute an out-of-focus routine OUTFS. In step #122, thein-focus indication is cancelled. In step #123, a query is made to seeif the reliability of the results of focus detecting calculation isexcessively low and the result of focus detection is unavailable, namelyif the contrast of the object is excessively low. When the response instep #123 is affirmative, the control program returns to step #105 toexecute the focus detecting routine CDINTA for the next focus detectionwithout driving the AF motor M₂. When the response in step #123 isnegative, the AF motor M₂ is actuated in step #124. When a decision madein step #125 is that the operation of the AF motor M₂ has ended, thecontrol program returns to step #105 to execute the focus detectingroutine CDINTA for the next focus detection. In step #124, the number ofdriving pulses ERRCNT by which the AF motor M₂ is to be driven iscalculated by using a equation: ERRCNT=DF0×KL, where DF0 is the amountof defocus of the photographic lens, and KL is a convergence coefficientpeculiar to the photographic lens. In step #125, the AF motor M₂ isdriven until the coincidence of the number of driving pulses applied tothe AF motor M₂ with the calculated number of driving pulses ERRCNT isdetected by an AFP signal monitoring the operation of the AF motor M₂.The convergence coefficient KL is peculiar to the focal length of thephotographic lens and is given from the photographic lens to the CPU 201through the serial communication between the photographic lens and theCPU 201. Then, steps #105 through #116 are repeated until thephotographic lens is brought to the in-focus position.

Steps subsequent to the detection of closing of the switch SW6 in step#119 will be described hereinafter. In step #126, a query is made to seeif the number of driving pulses ERRCNT is less than a constant NP1stored in the EEPROM 201f. When the response in step #126 is negative,the constant NP1 is reset as the number of driving pulses ERRCNT in step#127. When the response in step #126 is affirmative, a query is made instep #128 to see if the amount of defocus DF0 determined in step #116 isless than a constant DFC1. When the response in step #128 isaffirmative, namely, DF0<DFC1, the control program jumps to step #131 tostart the shutter release operation immediately. When the response instep #128 is negative, namely, DF0≧DFC1, a query is made in step #129 tosee if the number of driving pulses ERRCNT is less than "4". When theresponse in step #129 is affirmative, the control program jumps to step#131 to start the shutter release operation immediately. When theresponse in step #129 is negative, the AF motor M₂ is actuated in step#130. In steps #126 through #131, decisions are made to determinewhether or not the photographic lens is to be driven while the mirrorsare lifted up. As mentioned previously, the detected amount of defocusis compared with a predetermined limit value of defocus in step #116 todetermine whether or not the photographic lens is within in-focus. Whenthe limit value of defocus is very small, the decision is made highlyaccurately, whereas the decision takes much time due to variation infocus detection or camera shake, or undesirable minute oscillation ofthe photographic lens occurs. The detected amount of defocus variesmomentarily in taking a moving object, it is impossible to decidewhether or not the photographic lens is in-focus, if the limit value ofdefocus is excessively small. Accordingly, the limit value of defocus isdecided to flexibly cope with the variation in focus detection orvariation in the measurement of the amount of defocus due to themovement of the object relative to the camera can be absorbed. However,in this case the limit value of defocus remains as an error in focusing.To correct error, the photographic lens is driven during the upwardmovement of the mirrors thereby providing an automatic focusing camerawith high precision. The number of pulses available during the upwardmovement of the mirrors is limited to the constant NP1 (steps 126 and127) to curtail time up to shutter release operation if the focusingaccuracy is sufficiently high, namely, when DF0<DFC1 (step #128), orwhen the number of driving pulses ERRCNT is less than "4" (step #129),the shutter release operation is started immediately taking intoconsideration the driving accuracy of the AF motor M₂.

A series of steps of a shutter release operation control routine (step#201 and the following steps) including a mirror lifting operation, anexposure time control operation, a shutter mechanism cocking operationand a film winding-up operation will be described hereinafter withreference to FIG. 7.

A flag RMGONF is set to "1" in step #202 to indicate that the shutterrelease magnet RMg is being energized, supply of power to the AF motorM₂ is interrupted in step #203, and the shutter release magnet RMg, andthe shutter curtain holding magnets 1CMg and 2CMg are energized in step#204. After a latency in step #205, the shutter release magnet RMg isde-energized in step #206, and the flag RMGONF is set to "0". In steps#204 through #206, the main mirror 103 and the submirror 104 arereleased and the mirror lifting operation is started. While power issupplied to the shutter release magnet RMg in steps #202, #203 and #207,power is not supplied to the AF motor M₂. More specifically, the AFmotor M₂ is driven periodically by timer interrupt and the AF motor M₂is braked each time an AFP signal is generated. When the flag RMGONF=1,the actuation and braking of the AF motor M₂ is forbidden and the AFmotor M₂ is kept stopped. When the flag RMGONF is reset, the AF motor M₂is actuated automatically by timer interrupt. The foregoing steps areexecuted to avoid following possible disadvantage. The shutter releasemagnet RMg requires a large current for operation. If a current issupplied to the AF motor M₂ while the shutter release magnet RM_(g)needs to be energized, current supplied to the shutter release magnetRMg becomes insufficient, so that the shutter release magnet RMg isunable to release the shutter mechanism and the mirrors cannot be liftedup.

Upon the start of upward movement of the mirrors, the diaphragm stoppingmagnet FMg is energized in step #209. Consequently, an engagement ofdiaphragm diaphragm aperture of the photographic lens is released tostop down a diaphragm aperture. In step #210, pulse generated by thediaphragm aperture encoder 211 are counted. When the count of the pulsesmatches with a pulse count determined by the exposure calculation, themagnet FMg is de-energized to determine an opening of the diaphragmaperture in step #211. Then, in step #212, the shutter release magnetRMg is energized, and after a lapse of the predetermined time t₁, step#213 is executed. In step #213, power is not supplied to the AF motorM%₂ to prevent driving the photographic lens during exposure, and thenthe sequence motor M₁ is stopped in step #214. As mentioned above, thesequence motor M₁ is kept braked after a photographing cycle for thesecond frame during the continuous photographing operation until step#214 is executed to stop the sequence motor M₁. In step #215, the magnet1CMg restraining the preceding shutter curtain is de-energized to allowthe preceding shutter curtain to start travelling. After a latencycorresponding to the shutter speed in step #216, the magnet 2CMg forrestraining the trailing shutter curtain is de-energized in step #217 toallow the trailing shutter curtain of the focal plane shutter to starttravelling. Thus, the exposure operation is completed. In step #218, atime measured by a timer is stored in a memory TIME1. After a latencyt₁₈ in step #219 to hold the completion of travelling the trailingshutter curtain, a film winding routine (step #220) is executed.

Referring to FIG. 8 showing a film winding routine, the sequence motorM₁ is driven in the low-speed mode in step #221. After a predeterminedlatency for the rotating speed of the sequence motor M₁ to increase instep #222, the operating mode of the sequence motor M₁ is changed fromthe low-speed mode to the high-speed mode in step #223 to carry out theshutter mechanism cocking operation until the switch SW2 opens upon thecompletion of the shutter mechanism cocking operation. When the shuttermechanism cocking operation is completed, TTL photometric measurementbecomes possible, since the main mirror 103 and the submirror 104 areplaced at the lower operating position. In step #225, the photometricmeasurement is started. In step #226, the film releasing magnet AMg isenergized for a predetermined time t₆. Then, the routine is held in step#227 for a predetermined latency t₁₀ (in this embodiment, 30 msec) tostabilize the submirror 104. In step #228, a query is made to see if thecontinuous photographing mode is selected. When the response in step#228 is affirmative, the flag VLYF is set to "1" in step #229 toindicate the selection of the continuous photographing mode, and thenthe program goes to step #230 to execute the focus detecting routineCDINTA including step #105 and the following steps. When the response instep #228 is negative, the CPU waits until switch SW6 is open in step#231 and the program goes to step #230 to execute the focus detectingroutine CDINTA including step #105 and the following steps.

An automatic focusing operation for continuous photographing will bedescribed with reference to FIG. 9.

After the routine has gone from step #230 (FIG. 8) to step #105 toexecute the focus detecting routine CDINTA, the focus detectingcalculation and the exposure calculation are carried out in steps #105through #114 in a manner as described to FIG. 6. Then, in step #115, theprogram branches off to step #301 to execute a continuous photographingAF routine. In step #302, exposure calculation using data obtained byphotometric measurement in step #225 and serial communication areexecuted, and whereby correct exposure can always be achieved regardlessof variation in the brightness of the object during the continuousphotographing operation. Then, in step #303, a query is made to see ifthe switch SW1 is open. That is, only a single cycle of focus detectingoperation is allowed during the film winding-up operation to givepriority to the next shutter release operation in the continuousphotographing mode. Upon the detection of the opening of the switch SW1,namely, upon the detection of completion of the film winding-upoperation, the sequence motor M₁ is braked immediately in step #304. Instep #306, a query is made to see if the time spent for the filmwinding-up operation is longer than a predetermined time. Morespecifically, time after exposure shown by timer TIME1 is subtractedfrom the present time and the result is compared with the predeterminedtime. A time necessary for winding-up the film varies widely dependingon the tension of the film, the condition of the power supply or thenumber of frames. When the response in step #306 is affirmative, aprediction mode flag TF and an initial prediction flag T1STF are resetto "0" in step #307. The prediction mode flag TF is set to set at aprediction mode in which a correction corresponding to the movement ofan object is made in taking a moving object. When the response in step#306 is affirmative, namely, when the film winding-up operation requireda time longer than the predetermined time, the prediction mode flag TFis reset to "0", because interval between the successive photographingcycle is long and the correction corresponding to the movement of theobject includes an error.

In step #308, the result of focus detection is examined to decide if theobject is in a low contrast. When the decision in step #308 is negative,the program branches off to step #309 to set a low-contrast ignoringflag LIF to "0". The low-contrast ignoring flag is set to "1" tocontinue the continuous photographing operation ignoring a low-contrastcondition. In step #310, the last defocus speed (the moving speed of theimage of moving object on the image surface) VH0 is stored, and then thepresent defocus speed VH0 is determined in step #313. In step #313, thepresent defocus speed VH0 is calculated in the following manner. Thepresent amount of defocus DF0 has been obtained through detection andhas been stored in a memory before step #313. The last amount of defocusdetermined by the last focus detection is stored in the memory LDF instep #112 (FIG. 6). The position of the photographic lens at a momentcorresponding to the accumulation central time at which the amount ofdefocus DF0 is determined and stored in the memory MI as is described in#110 in FIG. 6. The position of the photographic lens at a momentcorresponding to the accumulation central time at which the previousamount of defocus LDF was determined is stored in the memory MIL. Avariation in the amount of defocus δDF caused by the movement of theobject is calculated by using an expression:

    δDF=DF0-LDF+(MI-MIL)/KL                              (1)

where DF0 -LDF is a variation in the amount of defocus, and (MI-MIL)/KLis the amount of defocus attributable to the movement of the focusinglens of the photographic lens in a period Δt between the lastaccumulation central time and the present accumulation central timedescribed in step #109 in FIG. 6, as

    Δt=TM-TML                                            (2)

From expressions (1) and (2), the present defocus speed VH0 isdetermined by:

    VH0=δDF/Δt

After the present defocus speed VH0 has thus determined in step #313,the program goes to #319.

On the other hand, when the decision in step #308 is affirmative, thatis, the contrast being low, a query is made in step #311 to see whetherthe low-contrast ignoring flag LIF is "0" or "1". When LIF=0, thelow-contrast ignoring flag LIF is set to "1", and the present amount ofdefocus DF0 and the number of driving pulses ERRCNT are cleared in step#312. When LIF=1 (step #311), the program branches off to a predictionmode cancellation routine OUTRV2 (step #314). In step #315, theprediction mode flag TF and the initial prediction flag T1STF, whichwill be explained afterward, are set to "0". Then, in step #317, acontinuous photographing mode flag VLYF is set to "0", and then theroutine jumps from step #318 to step #121 (FIG. 6) to execute theout-of-focus routine OUTFS. Thus, the continuous photographing mode iscancelled through steps #308 to #318 when the results of the twosuccessive focus detecting cycles indicate a low-contrast state. Then,the shutter release operation is prohibited until the photographic lensis brought into in-focus through the control operation according to thecontrol program of FIG. 6.

Thus, the foregoing routine allows the photographing operation once intaking a moving object even if the moving object moves off the focusdetecting area or a moving object having a low contrast is in the focusdetecting area. Accordingly, the possibility of missing a shutter chancein taking a momentary dramatic scene is reduced remarkably, and agreatly defocused state occurs at a low probability. The effect of theforegoing routines is significant particularly in the continuousphotographing mode, because most photographers desire to give priorityto the shutter release operation. Furthermore, since the continuousphotographing operation is interrupted until the photographic lens isbrought into in-focus when both the results of the two successivedetecting cycles indicate a low-contrast state, the shutter releaseoperation is never repeated continuously with the photographic lensdefocused greatly. Accordingly, the film will not be wasted even if theshutter release button is pressed accidentally or even if thephotographic lens is covered with the hand.

In step #312, the amount of defocus DF0 and the number of driving pulsesERRCNT are set at "0" because the amount of defocus DF0 and the numberof ERRNCT are indefinite since the object is in a low-contrast state.Since the defocus speed VH0 is unable to be calculated, the last defocusspeed VH0 is used without changing. In step #319, a query is made to seeif the prediction mode is selected. When the response in step #319 isnegative, namely, when the prediction mode flag TF="0", a query is madein step #320 to see if the defocus speed VH0 determined in step #313 isgreater than a constant VE1. When the response in step #320 isaffirmative, namely, when VH0>VE1, the limit value of in-focus INFZ isset at a constant FZREL1 in step #321 and, when the response in step#320 is negative, namely, when VH0≦VE1, the limit value of in-focus INFZis set at a constant FZREL2 in step #322. The limit value of in-focusFZREL1 is smaller than the limit value of in-focus FZREL2. That is, whenthe focusing speed VH0 is low, the object is considered to bestationary. In such a case, the limit value of in-focus can be largesince the variation in the amount of defocus is affected scarcely by themovement of the object. When the defocus speed VH0 is high, a smalllimit value of in-focus is selected since the variation in the amount ofdefocus is high. Since the limit value of in-focus is determined asdescribed above, the photographic lens is driven slightly for a stable,rapid continuous photographing operation when the object is stationary.A highly accurate continuous photographing operation with a small delayin the prediction operation can be achieved by selecting a small limitvalue of in-focus when the defocus speed VH0 is higher than apredetermined defocus speed VE1. The constants VE1, FZREL1 and FZREL2are stored in the EEPROM of the CPU 201 and are arbitrarily rewritable.

In step #323, a query is made to see if the limit value of in-focus INFZset in step #321 or #322 is greater than a detected amount of defocusDF0. When the response in step #323 is affirmative, it is consideredthat the photographic lens is in-focus position at a sufficiently highaccuracy, and the program goes to step #370 to decide if the switch SW6is closed. If the switch SW6 is closed, it means that a shutter releaseoperation is requested and therefore a shutter release operation for thenext photographing cycle is started in step #371. That is, since thephotographic lens is in-focus accurately, the shutter release operationis carried out for the next photographing operation in step #371 withoutdriving the photographic lens during the lifting up of the mirrors. Whenthe decision in step #370 is negative, namely, when the switch SW6 isopen, the program branches off the step #372 to execute a predictionmode cancelling routine OUTRV. In the prediction cancelling routineOUTRV, the continuous photographing mode flag VLYF and the initialprediction flag TISTF are set to "0" in steps #373 and #374, and thenthe routine jumps from step #375 to step #105 to execute the focusdetecting routine CDINTA for the next photographing cycle.

On the other hand, when the decision in step #323 is negative, namely,when the detected amount of defocus is greater than the limit value ofin-focus INFZ, a query is made in step #324 to see if the brightness ofthe object is low. More specifically, the brightness is determined onthe basis of a time required for accumulating charge in the CCD and again obtained by multiplying output data. When the response in step #324is affirmative, the magnification β of the image is calculated in step#325. In step #326, a query is made to see if the magnification β ofimage is greater than a constant BETALOCK. The program branches to step#333 when β>BETALOCK or goes to step #327 when β≦BETALOCK. In step #327,a query is made to see if the defocus speed VH0 is greater than aconstant RVMIN. The program branches off to step #333 when VH0≦RVMIN orgoes to step #328 when VH0>RVMIN. In step #328, a query is made to seeif the focusing speed VH0 is smaller than a constant RVMAX. The programbranches to step #333 when VH0≧RVMAX or goes to step #329 whenVH0<RVMAX. In step #329, a query is made to see if the direction of thepresent defocus speed VH0 is the same as that of the last defocus speedVH1. The program branches to step #336 when the response in step #329 isnegative or goes to step #330 when the response in step #329 isaffirmative. In step #330, a query is made to see if the initialprediction flag T1STF is "1". The program branches to step #335 when theresponse in step #330 is negative to set the initial prediction flagT1STF to "1". When the response in step #330 is affirmative, theprediction mode flag TF is set to "1" in step #331, and then the routinejumps to a prediction routine RNAFT1.

The prediction mode for correcting variation in the amount of defocuscaused by the movement of the object is determined through steps #323through #332. More specifically, when it is decided that the brightnessof the object is low in step #324, it is impossible to select theprediction mode because a comparatively long time is necessary forcharge accumulation in the CCD, noise signals increase, and hence it isimpossible to determine the defocus speed VH0 accurately. When it isdecided that the magnification of the image is large in step #326, it isalso impossible to select the prediction mode because camera shakeaffects the determination of the defocus speed VH0 significantly. Whenthe response in step #327 is negative, namely, when VH0≦RVMIN, it isimpossible to decide whether the variation in the amount of defocus isattributable to variation in focus detection or to the movement of theobject. Accordingly, to avoid erroneous correction, the prediction modeis not selected. Since the moving speed of the object is low, variationin the amount of defocus is negligibly small even if the variation iscaused by the movement of the object, and hence the focus condition neednot be corrected. When the response in step #328 is VH0≧RVMAX, it isconsidered that the variation in the amount of defocus is abnormallylarge. Such a condition is considered to be due not to the movement ofthe object, but due to the change of the object for another object, inother words it is decided that the camera is intendedly aimed at anotherobject. Accordingly, the prediction mode cannot be selected.

When the response in step #329 is negative, namely, when the presentdefocus speed VH0 and the last defocus speed VH1 are different from eachother in direction, it is decided the focus detecting operation isunstable or the object is moving irregularly. Accordingly, erroneouscorrection is highly possible and hence the prediction mode cannot beselected When the decisions in steps #323 to #329 are made twicesuccessively by executing steps #330, #331 and #335, the prediction modeis selected. Thus, it is surely decided whether or not the object is amoving object. Accordingly, there is no possibility of erroneouscorrection. The constants BETALOCK, RVMIN and RVMAX are storedbeforehand in the EEPROM of the CPU 201.

When the response in step #329 is negative, an unstable focus detectingoperation or unstable movement of the object is expected. Therefore, theprogram goes to step #336 to execute the prediction mode cancellingroutine OUTRV3. In step #337, the prediction mode flag TF, the initialprediction flag T1STF and the continuous photographing mode flag VLYFare set to "0", and then the program goes to step #338 to execute thefocus detecting routine CDINTA for the next photographing cycle in step#105 and the following steps. Since the routine is thus executed, thenext shutter release operation is forbidden and, as mentioned withreference to FIG. 7, the photographic lens is driven until the same isbrought into in-focus condition again. Accordingly, there is nopossibility of execution of the photographing operation before thephotographic lens is focused.

When the program branches from step #324, #326, #327, #328 or #330 tostep #333, the present amount of defocus DF0 is compared with a constantINFZE1 to see if DF0<INFZE1. When the decision in step #333 isaffirmative, the amount of defocus is not very large and the reliabilityof focus detection is high. The photographic lens can be in-focusposition at a sufficiently high accuracy even if the photographic lensis driven for focusing during the upward movement of the mirrors beforethe next shutter release operation. Therefore, the program branches tostep #382 for a photographic lens driving routine RNMTR, which isexecuted during the upward movement of the mirrors. When DF0≧INFZE1, theamount of defocus is comparatively large and hence possibility remainsthat the photographic lens cannot accurately be in-focus when the nextshutter release operation is started without correcting the in-focuscondition of the photographic lens. Accordingly, the program goes tostep #334 to execute the prediction mode cancelling routine OUTRV2. Whenthe amount of defocus is comparatively small, highly accurate automaticfocusing and a rapid continuous photographing operation can be achievedby driving the photographic lens during the upward movement of themirrors through steps #333 and #334. On the other hand, when the amountof defocus is comparatively large, the focus detecting operation isrepeated once again to focus the photographic lens, the photographiclens can automatically be focused at a high accuracy. When the programproceeds to the out-of-focus treatment OUTFS through prediction modecancelling routine OUTRV2 starting from step #334, the focus detectingoperation is performed again, as mentioned with reference to FIG. 6,after driving the photographic lens to cancel the present amount ofdefocus DF0, and hence the focusing condition of the photographic lenscan be quickly and accurately detected. The constant INFZE1 is storedbeforehand in the EEPROM 201f of the CPU 201 and arbitrarily rewritable.

The prediction routine RNAFTI (step #332 or #381) will be described withreference to FIG. 10. In step #340, a query is made to see if thepresent defocus speed VH0 and the last defocus speed VH1 are the same indirection. When the response in step #340 is negative, it is consideredthat the object has suddenly stopped, the direction of movement of theobject has changed or the camera has shaken in such a case, and theprogram branches to step #341 to execute the prediction mode cancellingroutine OUTRV3. Then, the automatic focusing operation is performeduntil the photographic lens is focused again. Thus, the photographiclens can be focused at a high accuracy without entailing erroneouscorrection even if the object stops suddenly, the direction of movementof the object changes or the camera shakes.

When the response in step #340 is affirmative, a query is made in step#342 to see if (VH0+VH1)/2 is greater than a constant AVESH. Theindication (VH0+VH1)/2 indicates a weighted mean ##EQU1## (as is derivedfrom step #310), where n is the number of loops, and VH_(i) is thedefocus speed determined in i-th cycle before the present detectingcycle. In step #324, a query is made to see if the weighted means isgreater than a constant AVESH. When the response in step #324 isnegative, the present defocus speed is changed for the weighted mean instep #343. When the response in step #342 is affirmative, the routinejumps to step #344. That is, variations in the result of focus detectionare absorbed by using the weighted mean when the defocus speed is lowfor stable focus correction. Since the variation of the amount ofdefocus increases substantially in inverse proportion to the square ofthe subject distance when the object approaches the camera at a constantspeed, the foregoing operation is effective for focus correction of ahigh response speed and less delay in following-up when the focusingspeed is high. The constant AVESH is stored beforehand in the EEPROM201f of the CPU 201. In step #344, the magnification β of image iscalculated and a query is made to see if the magnification of image isgreater than a constant BETALOCK2. As mentioned before, the influence ofcamera shake on the focusing operation is significant when themagnification of image is large. Therefore, the program goes to step#347 to execute the prediction mode cancelling routine OUTRV2. Theconstant BETALOCK2, which is set to be greater than the constantBETALOCK, is stored beforehand in the EEPROM 201f of the CPU 201. Instep #345, a query is made to see if the present defocus speed VH0 isgreater than a constant RVOUT. When the response in step #345 isnegative, the present defocus speed VH0 is sufficiently low, and hencethe program branches to step #347 to avoid erroneous correctionattributable to variation in the result of focus detection. In step#346, a query is made if the present defocus speed is lower than theconstant RVMAX2. When the response in step #346 is negative, it isconsidered that the defocus speed is very high and the predictioncorrection is unable to predict the variation of the focus entailing alarge amount of defocus. Accordingly, the program branches to step #347.In step #347, the prediction mode cancelling routine OUTRV2 is executedto cancel the prediction mode, whereby the next shutter releaseoperation is forbidden and the focus detecting operation is performedagain. Thus, the shutter release operation is forbidden when the objectmoves at a very high speed to avoid taking a photograph withoutprediction. Steps #344 through #346 prevent erroneous correction andensure highly accurate correction.

Then, in step #348, a prediction correction calculation 1 is executed tocalculate a number of driving pulses ERRNCT, which will be describedafterward with reference to FIG. 11. In step #349, a query is made tosee if the amount of defocus MDF determined by prediction correction issmaller than a constant INFZE2. When the response in step #349 isnegative, the program branches to step #350 to enhance the accuracy byexecuting a prediction mode cancelling routine OUTRV21 including step#316 and the following steps (FIG. 9). In the above steps, only thecontinuous photographing mode flag VLYF is set to "0", the predictionmode is maintained, and then the out-of-focus routine is executed. Theconstant INFZE2 is stored beforehand in the EEPROM 201f of the CPU 201.The constant INFZE2 is set to be greater than the constant INFZE1described in step #333 because the routine is unable to advance to step#351 if the amount of correction for prediction correction is not large.

Step #351 and the following steps are for the photographic lens drivingroutine to be executed during the lifting-up movement of the mirrorswhen the response in step #333 is affirmative or when the response instep #349 is affirmative. In step #352, a query is made to see if theswitch SW6 is closed. When the response in step #352 is negative, namelywhen the next shutter release operation is not requested, the programbranches to step #363 to execute the prediction mode cancelling routineOUTRV. When the response in step #352 is affirmative, query is made instep #353 to see if the number of driving pulses ERRNCT is not greaterthan the constant NP1. As mentioned above, (FIG. 6), the constant NP1 isthe number of driving pulses which can be generated during the lift-upof the mirrors. When the response in step #353 is affirmative, thephotographic lens can be driven properly during the upward movement ofthe mirrors. Then, the routine jumps to step #359.

When the response in step #353 is negative, a time corresponding to theduration of the lift-up of the mirrors is insufficient to drive thephotographic lens properly, and hence an additional time is requiredbefore starting the next shutter release operation. The time necessaryfor focussing the photographic lens by driving the AF motor M₂ dependson the condition of the power supply and the characteristics of thephotographic lens. To absorb the difference in the time necessary forfocusing the photographic lens attributable to those conditions, a fixedtime allowance of 40 msec is given before starting the next shutterrelease operation. When the number of driving pulses ERRCNT correspondsto a time on the order of 40 msec and less than the constant NP2, the AFmotor M₂ is actuated. When the number of driving pulses ERRCNT isgreater than the constant NP2, the focus detecting operation isperformed again. Thus, the focus of the photographic lens can becorrected accurately by a degree corresponding to 40 msec even in takinga moving object. Furthermore, even if the photographing operation iswithheld for 40 msec, a continuous photographing speed of 3 frames/secis reduced merely to 2.7 frames/sec, so that a desired continuousphotographing operation can be carried out substantially without anyrestriction. Still further, when the number of driving pulses ERRCNT isgreater than the constant NP2, the focus detecting operation isperformed again, which solves a problem in the conventional camera thatan error resulting from focus detection driving the photographic lensincreases without any restriction.

When ERRCNT>NP1 (step #353), a query is made in step #354 to see if theprediction flag TF is set to "1". When the response in step #354 isaffirmative (TF=1), a prediction correction calculation 2 forcalculating pulses corresponding to 40 msec in step #355. When theresponse in step #354 is negative (TF=0), step #355 is skipped. In step#356, a query is made to see if the number of driving pulses ERRCNT isnot greater than the constant NP2. When the response in step #356 isnegative, the program branches to step #364 to execute the predictionmode cancelling routine OUTRV2. When the program branches from step #349to step #350 for the prediction mode cancelling routine OUTRV2 or fromstep #356 to step #364 for the prediction cancelling routine OUTRV2 todrive the lens during the upward movement of the mirrors before the nextshutter release operation without performing the focus detectingoperation again, it is decided that the photographic lens is focused andthe in-focus indication is maintained.

Subsequently, in step #357, the AF motor M₂ is actuated. The routine iswithheld for a latency of 40 msec in step #358. When the response instep #353 is affirmative, the AF motor m₂ is actuated in step #359.Then, in step #360, a continuous shutter release routine RNRELESE isstarted. Since the camera is set for the continuous photographing mode,the routine is withheld for a predetermined latency of t₁₁ in step #361to stop the film perfectly, and then the shutter release operation isexecuted in step #362. As is obvious from the foregoing description, thevariation in the amount of defocus due to the movement of the objectmust be corrected in the prediction mode. Accordingly, the next shutterrelease operation is not performed with the photographic lens stopped.

The prediction correction calculation will be described hereinafter withreference to FIG. 11. In step #402, a query is made to see if the resultof focus detection shows that the contrast of the object is low. Whenthe response in step #402 is negative, a time T for correction iscalculated in step #403. The present, accumulation central time isstored in the memory TM. A time interval between the presentaccumulation central time and the next exposure operation is determinedby: TC -TM+70 (msec), where TC is the present time registered by thetimer and 70 msec is time required for mirror lifting-up. When thecontrast of the object is low, a time interval T between time when thelast exposure operation was performed and time when the next exposureoperation is to be performed is determined in step #404. As mentionedwith reference to FIG. 7, the time when the last exposure operation wasperformed is stored in the memory TIME1. Accordingly, the time intervalT is obtained by subtracting the time stored in the memory TIME1 fromthe present time TC and adding 70 (msec) to the remainder. That is, thetime T is calculated in step #403 on the basis of the present amount ofdefocus DF0 when the response in step #402 is negative, and when thetime T is calculated in step #404 on an assumption that the amount ofdefocus in the last exposure operation was zero when the response instep #402 is affirmative.

In step #405, the defocus speed VH0 is multiplied by the time T obtainedin step #403 or #404 to obtain a correction DF. Then, in step #406, aquery is made to see of the defocus speed VH0 is greater than a constantVVH. When VH0>VVH, namely, when the defocus speed is higher than apredetermined level, a query is made in step #407 to see if the objectis coming up to the camera. When the response in step #407 isaffirmative, the correction DF is multiplied by 1.25 in step #408,because the defocus speed increases in inverse proportion to the squareof the subject distance when the object is coming up to the camera alongthe optical axis of the photographic lens at a constant speed.Accordingly, when the object approaches the camera at a high speed, theamount of defocus increases in the time T obtained in step #403 or #404,and hence the correction DF is multiplied by 1.25 to correct thevariation in the amount of defocus attributable to the movement of theobject toward the camera. When the object is going away from the camera,the defocus speed decreases, and hence the correction DF is multipliedby 0.75 in step #409.

In step #410, a query is made to see if the present amount of defocusDF0 and the defocus speed VH0 are the same in direction. When theresponse in step #410 is affirmative, a corrected amount of defocus MDFis obtained in step #411 by adding the correction ΔDF to the amount ofdefocus DF0. When the response in step #410 is negative, a query is madein step #412 to see if DF0≦ΔDF. When the response in step #412 isaffirmative, a corrected amount of defocus MDF is obtained bysubtracting the amount of defocus DF0 from the correction ΔDF. When theresponse in step #412 is negative (DF0>ΔDF), the photographic lens mustbe driven in a direction reverse to the direction of the defocus speed,because the large amount of defocus DF0 is reverse to the direction ofthe defocus speed. When the response in step #412 is negative, stackinitialization is executed in step #414 to deal with an errorattributable to backlashes between the gears of a photographic lensdriving mechanism in reversing the photographic lens driving directionor the abnormal action of the object, and then the program goes to step#415 to execute the prediction mode cancelling routine OUTRV21.Consequently, the next shutter release operation is withheld and thefocus detecting operation is performed again. After the corrected amountof defocus MDF has been determined in step #411 or #413, the correctedamount of defocus MDF is multiplied by the convergence coefficient KL (acoefficient for converting the amount of defocus into correspondingnumber of driving pulses) in step #416 to determine a number of drivingpulses ERRCNT, and then the program returns in step #417.

Thus, the photographic lens can accurately be in in-focus position evenif the object is moving at a high speed regardless of the direction ofmovement of the object with respect to the camera. As is obvious fromthe description made with reference to FIG. 9, a correctioncorresponding to the movement of the object can accurately be determinedeven if the low contrast of the object is neglected once in steps #308through #312.

Timer interrupt and AFP interrupt will be described hereinafter withreference to FIGS. 12 and 13.

Referring to FIG. 12 showing a timer interrupt routine for driving theAF motor M₂, the CPU 201 is provided internally with an interrupt signalrequesting timer interrupt after a set time has passed. When the timerinterrupt signal is provided, the interrupt timer IT is reset in step#502 to make the interrupt timer IT generate next timer interrupt signalafter a set time from a moment when the present timer interrupt signalis generated. In step #503, a query is made to see if the flag RMGONF=1.When the response in step #503 is affirmative, namely when the shutterrelease magnet RMg is energized, the AF motor M₂ is stopped in step#505. When the response in step #503 is negative, namely, when RMGONF=0, the AF motor M₂ is actuated in step #504, and the program goes tostep #506 to return.

Referring to FIG. 13 showing an AFP interrupt routine to be executed atthe trailing edge of an AFP signal, the number of driving pulses ERRCNTis reduced by "1" in step #602 upon the generation of the AFP signal. Instep #603, a query is made to see if the number of driving pulses ERRCNThas decreased to zero and thereby the AF motor M₂ being stopped. Whenthe response in step #603 is negative, the interrupt timer IT is resetin step #604. In step #605, a query is made to see if the flag RMGONF=1.When the response in step #605 is affirmative, namely, when the shutterrelease magnet RMg is energized, the AF motor M₂ is stopped in step#608. When the response in step #605 is negative, the AF motor M₂ isbraked in step #606, and then the program goes to step #607 to return.On the other hand, when the response in step #603 is affirmative, the AFmotor M₂ is stopped in step #609, timer interrupt is forbidden in step#610, AFP interrupt is forbidden in step #611, and then the program goesto step #607 to return.

Thus, the AF motor M₂ is driven in the timer interrupt mode and the AFPinterrupt mode, and the AF motor M₂ is stopped while the shutter releasemagnet RM_(g) is energized.

Referring to FIG. 14, another embodiment of the present invention isdescribed. "AF motor OFF" in the step #609 of FIG. 13 is replaced by thestep #709 "AF brake" in FIG. 14. In this embodiment, if the power supplyto the AF motor is turned OFF while the release magnet (RMg) isconductive and when the lens is moved by a prescribed amount in order toprevent driving of the lens by the inertia of the AF motor (ERRCNT=0,#703), then the brake is applied to the AF motor. Therefore, the lens isstopped exactly at the prescribed position, preventing defocus.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. A camera, comprising:(a) a first actuator; (b) asecond actuator; (c) power supply means for supplying electric power tosaid first and second actuators; (d) first controlling means for causingsaid first actuator to operate a predetermined operation; (e) suspendingmeans for suspending said power supply to said first actuator withoutbraking said first actuator, said suspending means allowing said firstactuator to continue operation due to inertia; and (f) secondcontrolling means for controlling said suspending means such that whensaid power supply to said first actuator is suspended, said power supplyis applied to said second actuator in order to actuate said secondactuator in advance of completion of the predetermined operation of saidfirst actuator, and for resuming the power supply to said first actuatorto complete the remaining operation of said first actuator after saidsecond actuator has finished operation.
 2. A camera according to claim1, wherein said first actuator is a motor and carries out a prescribedoperation.
 3. A camera according to claim 2, wherein said secondactuator comprises an electromagnet.
 4. A camera according to claim 1,further comprising:a lens for focusing an object; and shutter releasingmeans for exposing a film; wherein said first actuator comprising amotor for driving said lens, and said second actuator comprises anelectromagnet for driving said shutter releasing means.
 5. A cameraaccording to claim 4, wherein said controlling means suspends powersupply to said motor immediately before exposure of said film.
 6. Acamera, comprising:(a) a first actuator; (b) a second actuator; (c)power supply means for supplying electric power to said first and secondactuators; (d) suspending means for suspending said power supply to saidfirst actuator without braking said first actuator, said suspendingmeans allowing said first actuator to continue operation due to inertia;(e) controlling means for controlling said suspending means such thatsaid power supply to said first actuator is suspended before said secondactuator is actuated, and for resuming the power supply to said firstactuator after completion of operation of said second actuator; (f) adriven member driven by said first actuator; (g) monitoring means fordetecting an amount of movement of said driven member and for outputtinga detecting signal when the amount of movement reaches a prescribedvalue; and (h) movement stopping means responsive to said detectingsignal for stopping movement of said first actuator.
 7. A cameraaccording to claim 6, wherein said first actuator comprises a motor, andsaid second actuator comprises an electromagnet.
 8. A camera accordingto claim 7, further comprising:a lens for focusing an object; andshutter releasing means for exposing a film; wherein said first actuatorcomprises a motor for driving said lens, and said second actuatorcomprises an electromagnet for driving said shutter releasing means. 9.A camera according to claim 8, wherein said controlling means suspendspower supply to said motor immediately before exposure of said film.